Electrochemical batteries (“batteries”), which provide a stable, continuous electrical current to a circuit from a chemical energy source, have been in use at least since the early 1800s, when Alessandro Volta invented the voltaic pile. In a battery, internal chemical reactions (such as an oxidation/reduction reaction) drive or liberate electrons (and, therefore, a negative net charge) at an electrical contact called an anode, and a positive charge to another electrical contact called a cathode. By bridging the anode and cathode with an electrical conductor, a circuit is formed, which may include an appliance, and electrical current flows from cathode to the anode, powering such an appliance. Unless and until such an electron circuit flow occurs out of the anode, the internal chemical reaction is limited due to the buildup of charged products intercalated at the anode. Typically, the potential reaction energy that is not yet occurring comprises a major part of the battery capacity, and the time that the reactions require to take place serve to smooth or “buffer” electrical energy delivery at a steady current and voltage. As the battery discharges its current, the internal chemical reaction, and the battery itself, is eventually depleted and must be replaced or recharged to maintain delivery of electrical power in the circuit.
The first rechargeable batteries were lead-acid batteries, originating in the 1850s. By passing an electrical current in the direction opposing its discharge current, some of the current-producing chemical reaction is reversed (and the charged state of the battery is restored) in a rechargeable battery. To this day, rechargeable batteries face difficult challenges and are thought by many to be a relatively impractical power source for certain applications requiring high-power and high-energy-capacity. Among other challenges, each type of rechargeable battery has its own unique discharge and optimal recharging profile (a “charging curve”), requiring specialized hardware to control, and requiring significant time to carry out. Further complicating the issues, due to manufacturing inconsistencies, each individual battery of the same type has its own unique characteristics, including capacity, voltage, internal resistance and other differences from other individual batteries—even in the same production run. In larger-scale applications of rechargeable battery cells or other units (as in electric or hybrid vehicles, where arrays of cells or modules may be implemented), manufacturers may seek to test battery units and group those with very similar characteristics, to avoid or limit mismatches that might lead batteries to become out of sync with one another in terms of charge state or capacity over several charge cycles. But some mismatch still occurs despite these efforts, and sub-optimal charging and discharging results, for at least some units. If sub-optimal discharge or charging takes place, such as overcharging or overdischarging cells beyond their ideal levels, a significant amount of power may be lost as waste energy, and injury may occur to the battery, appliance and bystanders. See, e.g., Consumer Product Safety Commission, PC Notebook Computer Batteries Recalled Due to Fire and Burn Hazard, Recalls Release No. 09-035 (Oct. 30, 2008), available at http://www.cpsc.gov/en/Recalls/2009/PC-Notebook-Computer-Batteries-Recalled-Due-to-Fire-and-Burn-Hazard/. Virtually all mainstream battery labels in everyday households instruct laymen on how to avoid the risks of explosion and leakage from common misuse, such as placing the battery into an appliance backwards. See, e.g., Proctor & Gamble, Duracell Duralock 1.5 Volt AA Alkaline Battery Product Label (EXP 2022). The most effective batteries in terms of capacity, weight burden and discharge profile are often the most dangerous in the event of misuse, perhaps due to their less tested, limits-pushing technology. For example, the danger of fire is presently greater for much lighter and more capacious Lithium Polymer and Lithium polymer/ion hybrid batteries than for their older Lithium ion counterparts.
Even where catastrophic events do not occur, mismatched batteries placed together in parallel or series arrays may lead to sub-optimal performance. For example, when a battery with much higher capacity and charge is paired with a battery of low capacity and charge in series, the weaker battery may greatly limit the voltage and current of the array. When placed in parallel, such mismatched batteries, if sufficiently unbalanced, may lead to the stronger battery (or batteries) recharging the weaker battery.
Approaches to address the effects of charge imbalances have included many active charge-level management systems, several of which operate on a cell-by-cell basis. In some instances, such systems discharge cells that are relatively overcharged, or selectively continue to charge cells that are undercharged, or otherwise individually charge each cell to an appropriate level, in an effort to achieve a similar state of all cells. See, e.g., U.S. Pat. No. 5,617,004, to Kaneko, U.S. Pat. No. 7,598,706, to Koski and Lindquist, and U.S. Pat. No. 8,143,852, to Murao.
In some instances, external batteries, capacitors and switches, among other hardware, may assist such systems in redistributing the charged states of the individual cells. Cells with higher voltage are sometimes used to charge lower voltage cells. See, e.g., U.S. Pat. No. 5,900,716, to Collar et al. Some such systems are bi-directional, to exploit at least some common structures in charging and discharging functions, and decrease auxiliary wiring and structural manufacturing costs. See, e.g., U.S. Pat. No. 5,656,915, to Eaves. Some approaches also include cell bypass modules, to isolate a cell for recharging or remove a damaged cell from a series. See, e.g., id., U.S. Pat. No. 5,897,973, to Stephenson and Palmore. Additionally, some systems attempt to ameliorate waste due to the discharge of high cells (if applicable to the balancing approach) by applying greater loads to those cells. See U.S. patent application Ser. No. 10/900,502, Publication No. 20060022639A1, to Moore.
It should be understood that the disclosures in this application related to the background of the invention, in, but not limited to this section titled “Background,” do not necessarily set forth prior art or other known aspects exclusively, and may instead include art that was invented concurrently or after the present invention and conception, and details of the inventor's own discoveries and work and work results.